As the title suggests, I plan on finding out the burst pressure of run of the mill steel pipe that you find at hardware stores, likely 2" diameter.

As _Fnord's inconclusive test showed, it takes a hell of a lot of pressure to destroy that stuff, so this test could prove to be difficult and expensive to conduct, but I do have some ideas.

My first planned test is to see what kind of a hybrid mix it takes to destroy a steel hybrid. For the sake of simplicity and carnage, I'll probably use pure O2 and MAPP gas. I plan on an oxygen delivery system capable of 250 psi, so there shouldn't be any problems with available power. I hope to avoid DDT by using a short, fat chamber, so that my results are based purely on pressure generated, not on a rapid spike. This test will also include a 0-3000 psi peak pressure gauge setup, which would be attached with SCH 80 1/2" steel, and supported to avoid losing the gauge if the chamber is converted to shrapnel.

I have some of this setup already, and will be testing it in the near future on small diameter ABS pipe to see how well it works (currently my O2 setup is only capable of ~60 psi delivery pressure, so probably not any ruptured steel pipe yet.

My second planned test is to attempt to find the failure pressure of common steel parts used in a pneumatic launcher, likely in 1" size. The setup would likely utilise steam pressure, which would be easy to generate and gauge. Just set up the fire and retreat to a safe distance.

These tests may not have a high degree of accuracy, but after seeing just how difficult it is to rupture steel pipe without solid explosives, I made it one of my goals to do so ( other launcher related goals include firing a 1 pound projectile at >1000 fps, putting a single airsoft round through 1/2" plywood, and breaking Mach 2 with a launcher).

Please give me any useful suggestions relating to making these tests easier, cheaper, safer, or more accurate.

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Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.

Seriously, why do we even build these launchers? We spend hundreds of dollars on parts which we can never resell, just to shoot household objects out of plumbing parts.

After you know the burst pressure, you can see what really is safe, and what isn't. In this case, we have a good idea of the theoretical burst pressure, but we've never had a steel launcher fail, so we don't know how much farther we can safely go. This is supposed to be for the benefit of the spudding community, and if you don't have anything positive to contribute, you really don't need to contribute anything at all.

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Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.

homedepotpro wrote:why? who would benefit from those results. Fnord already showed that you can't rupture steel pipe at even an 11x mix. who even goes up that high?

I sure as hell would if my BBQ igniter could produce a spark at over 80 psi.
DYI, having a short, fat chamber may not work the best, because the steel pipe fittings in 2" and up are usually at least twice as thick as the Sch 40 pipe. Make sure at least 4 inches of the pipe itself are exposed.

In the US, what you are proposing is almost certainly illegal. So watch your ass.

My wild ass guess is that it is not possible to rupture steel pipe, even with MAPP + oxygen. As pressure rises the burn rate slows down. The slower the burn rate the more time there is for heat (hence pressure) to be lost to the chamber walls. Net result, you loose energy to heat conduction too fast for the pressure to ever get high enough to rupture the pipe.

Fnord already showed that you can't rupture steel pipe at even an 11x mix. who even goes up that high?

Try asking that questiong again in 5 years.
With the success* of the test, I plan on making an extreme mix rifle sometime within the next 6 months that might even go past 11x.

Noname, have you considered using an ignition coil? It's really quite easy and cheap especially if you have a junkyard around. My ignition setup costed me nothing.

*Success in this case means I (you) have a better understanding of what steel can withstand. Even though the ultimate goal of destroying the pipe failed, I've certainly layed waste to the "dont go above 4x or your head will A Splode!!11!" myth.

Hmmm... I look forward to seeing what kind of questions we will be wondering about in September 2008...

Jimmy's concern is valid, and I don't really know how to avoid that problem. If my test fails to rupture the pipe it will only benefit me, since I would then have a working 17x Oxy-MAPP hybrid. (seems kind of crazy when you think about it). I thought I had heard somewhere that burn rate increases as the initial pressure rises, but Jimmy knows a lot more about the physics of gaseous combustion than I do.

Killjoy, I wish you luck with the oxy-hydrogen endeavour. I had come up with an idea for a high pressure O2-H2 hybrid a while ago, but never though that my building materials would survive it. The only problem in that case could be detonation, which probably would destroy the pipe.

Noname, when I said short and fat, I meant a chamber approximately 2" x 6". This is to attempt to avoid detonation.

Recent tests have shown that DDT is more difficult to create than previously thought, especially in the low volume steel chambers that are currently the most common in hybrids.

As far as the laws surrounding this project go, I'm not really sure if this would be classified as a pipe bomb or not, but it certainly won't be as loud as the 350 psi, 2" bore burst disk cannon in my back yard (which will be posted in a matter of days), and I plan on keeping it as inconspicuous as possible. The testing on the ABS pipe should be posted within 2-4 weeks, depending on the cash flow situation and workload.

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Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.

Killjoy, I wish you luck with the oxy-hydrogen endeavour. I had come up with an idea for a high pressure O2-H2 hybrid a while ago, but never though that my building materials would survive it. The only problem in that case could be detonation, which probably would destroy the pipe.

Yeah, but you never know what will really happen till you try it, hopefully nothing bad. Thanks though.

As far as the laws surrounding this project go, I'm not really sure if this would be classified as a pipe bomb or not, but it certainly won't be as loud as the 350 psi, 2" bore burst disk cannon in my back yard (which will be posted in a matter of days), and I plan on keeping it as inconspicuous as possible. The testing on the ABS pipe should be posted within 2-4 weeks, depending on the cash flow situation and workload.

After searching for 15 minutes or so (and I'm probably being watched by the FBI now, but...), Technically, it is not a pipe bomb, since its intended use is not as a pipe bomb (not made or meant to explode), and the flammable mixture is propane, which isn't necessarly explosive (since the common definiton says a pipe bomb is filled with an explosive mixture) it just burns, and it is for educational purposes too.
Best to keep it low profile though, since I'm sure some ignorant/arrogant prosocuter or person of power would "enjoy" taking a closer look at this experiment.

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Stanford Class of 2012

"In the end our society will be defined not only by what we create, but what we refuse to destroy"- John Sawhill

DYI wrote:I thought I had heard somewhere that burn rate increases as the initial pressure rises, but Jimmy knows a lot more about the physics of gaseous combustion than I do.

For a laminar flame front of most hydrocarbon fuels, in air, the flame front speed accerates with rising temperature and decelerates with rising pressure. (The pressure dependence is back-assward from what I would have guessed.)

Of the two affects, pressure and temperature, the temperature is a much stronger accelerating affect than is the decelerating affect of rising pressure.